1. Field of the Invention
The present invention pertains to expansion joints for insulated fluid storage tanks. More particularly, the present invention pertains to expansion joints on thermally insulated fluid storage tanks. More particularly still, the present invention pertains to a expansion joints on fluid storage tanks, including upper surfaces of said fluid storage tanks, and a method for installing such expansion joints.
2. Brief Description of the Prior Art
The installation and use of thermal insulation on storage tanks is well known. Such thermal insulation can be particularly beneficial on large, flat-bottomed tanks used for storing materials that are sensitive to temperature fluctuations. Among other benefits, the insulation acts to reduce heat loss or gain of the materials stored within such tanks.
Existing methods for insulating storage tanks frequently employ interlocking panels of insulation and jacketing material. In one common method of insulating fluid storage tanks, a first layer of insulation panels is installed on the outer surfaces of a storage tank. Thereafter, a second layer of jacketing material is installed around the insulation material, encasing the insulation panels and securing such insulation panels in place around such storage tank.
Such insulation and jacket panels, typically fabricated to fit the specific dimensions of a particular storage tank, can frequently include flanges that are mechanically connected to adjacent panels. In one common prior art method, mechanical seams are used to join adjacent panels and create a homogeneous outer jacket that secures insulation panels to a storage tank. Ideally, such panels prevent moisture ingress, provide wind resistance and thermal insulation, and have inherent expansion and contraction properties to account for thermal expansion and contraction effects.
Depending on the operating temperature of a tank, as well as the ambient temperatures in the environment surrounding such tank, tank insulation systems may require installation of at least one expansion/contraction joint (“expansion joint”), especially on the roof or upper surface(s) of such tank. Such expansion joints absorb thermal expansion or contraction of the storage tank itself, as well as expansion and contraction of insulation materials and metal jacketing or cladding around such tank.
Such expansion joints are especially useful when installed on roofs or upper surface(s) of storage tanks because such areas can be particularly susceptible to thermal expansion and contraction. However, existing expansion joints are typically prone to water intrusion, as rain water and/or moisture from other sources have a tendency to collect on the upper surfaces of storage tanks.
In most cases, roofs and other upper surface(s) of storage tanks are manufactured using a number of steel sheets or other components that are welded or otherwise jointed together to form a substantially continuous surface. Although such steel sheets or other manufacturing components are generally rigid, and typically have at least a gentle slope from the center toward the outer edges of a roof to facilitate water drainage, low spots or depressions can nonetheless form at different places, particularly along the relatively large surface area of a tank roof; rain water and moisture from other sources can frequently collect and pond in such low spots. If an expansion joint happens to intersect or be in close proximity to such a low spot, water or moisture that collects at such a low spot can enter the expansion joint. Even without such low spots, driven rain and other precipitation can often directly invade conventional expansion joints.
Water or moisture entering a conventional expansion joint can often intrude into the space formed between the outer surface of a storage tank and the inner surface of the insulation materials (typically panels) covering said tank. Such water or moisture frequently results in oxidation or corrosion of the storage tank. In many cases, water in this space can also flow outward off the upper surface of a tank, over the outer perimeter edge of the tank roof, and collect behind vertical insulation panels disposed around the side walls of said tank. If enough water collects behind such insulation panels, the weight of such water can cause a catastrophic failure of the insulation system and its means of attachment to an underlying storage tank.
In an attempt to direct water away from expansion joints, prior art methods have included the construction of raised dam-like features near such expansion joints. In many cases, such dam-like features are formed by turning up panel ends near the expansion joint. Ideally, any water collecting near an expansion joint will be prevented from entering such expansion joint by the raised dam-like members and, as a result, pond away from the expansion joint and eventually run off or evaporate from the tank roof. Additionally, elongate cap members (typically constructed of metal) are fabricated and installed over expansion joints. However, such efforts have proven to be ineffective at keeping water and moisture out of expansion joints, especially with respect to wind-driven precipitation or moisture.
Thus, there is a need for an improved expansion joint that beneficially prevents water (in the form of rain, precipitation or otherwise) and moisture from entering such expansion joint and contacting insulation materials in proximity to said expansion joint. Said expansion joint should prevent water and moisture from intruding into the spaces formed between insulation panels and the outer surface of a storage tank, as well as spaces existing between insulation and jacketing materials.